The proposed work has three major objectives: 1) The isolation of drug resistant and auxotrophic mutants in order to increase the number of chromosomal markers until each linkage group carries several genetically useful mutants. This will simplify the linkage assignment and eventual mapping of developmental mutants. A substantial effort will be made to obtain a chemically defined growth medium suitable for the isolation of auxotrophic mutants. 2) The isolation of mutants with defects in the process of cell adhesion. All such mutants will be assigned to linkage groups and ultimately mapped. Procedures for the isolation of cell membranes will be developed and attempts to localize the biochemical lesion(s) will be made. 3) The mutant FR-17 will be examined and an attempt will be made to determine how the wild-type allele functions in development. An effort will be made to isolate mutants allelic to the one that is known as well as related but non-identical mutants. A hypothesis involving negative control of early development will be tested.